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EPRI Assessment of PISCES Water Characterization Studies 

Introduction 

The US EPA recently announced its intentions to conduct a two-year study to determine 

whether the Steam Electric Categorical Effluent Guidelines should be revised. An element 

of EPA's two-year study will involve data collection at various sites to provide data on 

waste streams from power utilities. To inform the EPA in its Effluent Guidelines Study, the 

Electric Power Research Institute (EPRI) is providing the results from its earlier research 

studies characterizing power plant wastewater streams at seven sites. Much of EPRI' s 

research efforts were conducted in the late 1990s and early 2000s and often for varying 

objectives, some of which were site-specific needs. Thus EPRI believes it is critical to 

provide our perspectives on the results of these studies. 

The following document is an evaluation of the wastewater data obtained during the 

PISCES wastewater field studies. The evaluation includes a critical assessment of the data 

quality and collection techniques for liquid samples in the PISCES data set collected in the 

late 1990s and early 2000s as compared to data quality and collection techniques for samples 

collected by today's sampling and analytical protocols. This evaluation reflects how 

representative the data set is of Steam Electric Utility industry as a whole, and how 

representative the PISCES data from the late 1990s are compared to plant operating 

conditions at those facilities today, and includes key lessons learned in attempting to 

characterize power plant waste streams accurately. 

PISCES Overview 

In 1988, EPRI initiated the Power Plant Integrated System-Chemical Emissions Study 

(PISCES) project to characterize the distribution of trace substances in air and liquid streams 

from fossil-fuel-fired electric utility power plants. The initial focus of this effort was on flue 

gas (air) emissions, in response to the Clean Air Act Amendments. At the completion of this 

effort, EPRI shifted its focus to expand the level of knowledge of trace substance 

concentrations in internal and effluent waste water streams in fossil-fuel power plants. 

EPRI along with various host utilities co-sponsored sampling studies of wastewater streams 

at seven power plants during the late 1990s and early 2000s. To maintain consistent 

sampling and analytical protocols throughout the research project, EPRI selected CH2M 

HILL to conduct these field studies. The methods of collection and analyses utilized were 

chosen in an effort to minimize contamination and enhance analytical sensitivity while 

maintaining accuracy and precision. Investigators characterized ash sluice wastes, flue gas 

desulfurization (FGD) scrubber wastes, plant sump discharges, cooling tower blowdown, 

coal pile runoff, water treatment residuals, and plant intake water at seven stations. 

Key PISCES Characterization Observations and Lessons Learned 

The PISCES characterization studies were of limited scope (only 7 facilities) and duration. 

Therefore, conclusions based on the studies may not be generally applicable to the rest of 

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the industry. However, this section summarizes the key lessons learned during the PISCES 

studies: 

• Ash ponds are generally effective in removing TSS and particulate-bound metals. 

Removal of dissolved trace metals is more complex and site-specific. 

• Ash pond pH appears to be related to the calcium and sulfate concentration in the fly 

ash. 

• Fly ash sluicing is a major source of metals to the ash pond. 

• Coal properties and boiler types affect fly ash characteristics and constituents. 

• Clean methods provide more reliable characterization of the ash pond effluent and other 

streams with trace metal levels. 

• Daily variability of the NPDES and ash pond effluent appears to be relatively minor due 

to the residence times and mixing associated in the ash pond (will not likely change 

daily, but will change on a weekly or monthly basis). 

• Seasonal variability can be significant and is often related to coal properties and other 

plant operational changes (e.g., operation of an SCR/SNCR), in addition to natural 

weather effects such as rainfall. 

• Sampling methods for difficult streams were developed, such as fly ash sluice water. 

This will be summarized in more detail in a separate EPRI document "Sampling & 

Analytical Plan Guidance for Water Characterization of Coal-Fired Steam Electric Utility 

Facilities" to be provided to EPA. 

Do the Data from the PISCES Studies Represent the Sites Today? 

For the PISCES wastewater characterization studies, EPRI partnered with various host 

utilities who voluntarily participated and provided substantial financial support to conduct 

these detailed measurements. Because of this, the host utility generally had specific 

objectives to address. In addition, due to the uniqueness of each power plant design and 

wastewater management approach, each site test plan was developed in close coordination 

with the host utility. To help encourage participation in these wastewater characterization 

studies, EPRI agreed to not identify the name of the utility and the power plant. A 

description of the field studies at the 7 power plants is provided in Table 1. 

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Table 1. Summary Description of EPRI PISCES Water Characterization Sites 

Ash Recent Known 

Site Coal Boiler FGD SCR Handling Comments Plant Changes 

Added SCRs, 

Periodically wet SNCR, and FGD. 

A E. Bit. Tangential N N Dry ash handles Different coal. 

Added SCR. 

Planned FGD 

(2010). Units 1-4 

to be replaced with 

new unit. Unit 5 

Focus on now sells most of 

impacts of its fly ash, and now 

specific coal functions similar to 

B E. Bit. Tangential N N Wet sources drv ash handling. 

Added SCR and 

Focus on FGD. Different 

impacts of coal. 803 injection 

specific coal no longer 

c E. Bit. Wall N N Wet sources employed 

Added SCR, 

Venturi upgraded existing 

scrubber; once- FGD, added pH 

through water control to waste 

0 E. Bit. Tangential y N Wet management water 

Zero surface 

water discharge 

with pond 

recycle to Added SCRs and 

E E. Bit. Wall y N Wet cooling lake additional FGDs. 

Venturi Added SCRs and 

scrubber; once- additional new 

through water generation onceF E. Bit. Cyclone y N Wet management through FGD 

E. Bit+ Focus on 

G W. Sub Cyclone N N Wet ammonia Added SCR 

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Some sites chose to participate in the PISCES program to address specific wastewater issues. 

Below is a summary of each site's objectives which may affect the uniqueness of the site: 

• Sites A and B are summarized in PISCES Water Characterization Field Study: Sites A 

and B (TR-1 08890, Volumes 1 and 2). Site A employed dry ash handling. However, 

the dry ash handling system periodically experienced operational issues, at which time 

the ash was wet sluiced. Selective catalytic reduction (SCR), selective non-catalytic 

reduction (SNCR), as well as wet FGDs has been installed at the various units. The coal 

supply at Site A has changed, and a different coal is now being burned. For Site B, the 

coal/fly ash tended to yield high arsenic and selenium concentrations in the ash pond, 

and thus these concentrations are likely to be in the high end of the range for the overall 

industry. The coal supply at Site B has changed, and a different coal is now being 

burned. An SCR has now been installed at Site B, and plans have been made to shut 

down Units 1-4 and to repower with a new unit. Site B Unit 5 now sells most of its fly 

ash, and now functions similar to dry ash handling facility. 

• Site Cis summarized in PISCES Water Characterization Field Study: Site C (TR-108891, 

Volumes 1 and 2). At Site C, studies were performed to assess the relationship between 

acidic coal, cationic metals, and ash pond performance. At the time of the studies, this 

site employed S03 fly ash conditioning which acidified the fly ash sluice water. This site 

currently does not burn this acidic coal, and S03 injection is no longer utilized. SCR and 

wet FGD have been installed at the site. 

• Site Dis summarized in PISCES Water Characterization Field Study: Site D (TR108892, Volumes 1 and 2). Two units employed FGDs with combined particulatejS02 

capture as well as a once-through water management system; the data are of limited use 

for characterizing recycled water management or newer wet FGDs. SCR and an 

upgraded FGD system have now been installed at the site, as has added ash pond pH 

control system. 

• Site E is summarized in PISCES Water Characterization Field Study: Site E (TR-112433, 

Volumes 1 and 2). This site does not have an NPDES regulated discharge nor an NPDES 

permit. Recycling of the ash pond and other waters into a cooling lake is employed at 

the site. Additional FGDs as well as SCRs have also been installed at the site. 

• Site F is summarized in PISCES Water Characterization Field Study: Site F (TR114966). In this study, aqueous ammonia was directly added to the ash pond to 

simulate ammonia flue gas slip from the SCR, so data are not representative of actual 

operating conditions. Two units employed FGDs with combined particulatejS02 

capture as well as a once-through water management system; the data are of limited use 

for characterizing recycled water management or newer wet FGDs. The FGD pond 

discharged to the ash pond, so the ash pond water was affected by addition of dissolved 

constituents of FGD wastewater. FGD water use was higher than more modern FGDs, 

so constituents may be less concentrated. SCRs and a third FGD have been installed at 

the site. 

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• Site G is summarized in PISCES Water Characterization Field Study: Site G (1001404). 

The focus of this study was ammonia in the ash pond, so much less metals data were 

collected. Similar to Site F, aqueous ammonia was directly added to the ash pond to 

simulate ammonia flue gas slip from the SCR, so data are not representative of actual 

operating conditions. SCRs have been installed at the site. 

Do the PISCES Sites Represent the Current Steam Electric Industry? 

A goal of the PISCES program was to characterize wastewater streams from across the 

utility industry. The PISCES program included only seven sites. This compares to about 

500 coal-fired power plants in the U.S. Using a small sub-set (~1 %) has inherent limitations 

on the representativeness of the industry as a whole. Further, these sites were volunteers 

and several chose to participate because of unique needs at the site. Further, because 

objectives varied by site, the data collected differed between sites. 

In evaluating whether the PISCES sites represent the industry as a whole, it is useful to 

understand what factors may affect wastewater. The major factors that may influence a 

station's liquid and solid waste streams include: 

• Fuel characteristics: Variation in coal characteristics when either bottom of fly ash is wet 

sluiced can affect wastewater pH and metals content in ash ponds. Dry stack facilities' 

runoff would also be influenced by coal properties but handling is different and 

discharge quantities generally lower than those from sluicing ponds. The origin of the 

coal as well as whether the coal is washed may influence the constituents seen in 

wastewater effluent and other internal water streams. 

• Ash handling system: Wet sluicing of fly ash will result in increased introduction of 

metals and other constituents to ash pond water compared to sites that use dry fly ash 

handling. 

• Air emission control technologies can affect wastewater: 

Flue gas desulfurization (FGD) scrubbers capture volatile metals along with acid 

gases. FGDs can also add a significant suspended solids load, depending on the 

FGD' s liquid-solid separation process. FGD design and operations, such as using 

lime or limestone, age, recycled or once-through scrubber design, oxidation 

approach, scrubber additives, make-up water source and management, and coal 

chloride concentrations, are other factors which affect FGD performance and, 

therefore, wastewater loads. 

- Particulate matter (PM) control devices such as cold-side electrostatic precipitators 

(ESPs), hot-side ESPs, and fabric filters can impact wastewater if these discharges are 

wet handled as these devices capture fly ash which contains trace metals. 

Ammonia slip from Selective Catalytic Reduction (SCR) or Selective Non-Catalytic 

Reduction (SNCR) can enter the plant wastewater if fly ash is wet sluiced and if slip 

is significant. However, data from newly installed plants indicate that many operate 

with little or no slip. 

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• 

• 

• 

Geographical location: The geographic location impacts the availability of nearby water 

sources, impacts the amount of water used and therefore the amount of water 

discharged as effluent. Geographic location also affects the potential coals that may be 

burned and quality of source water which has the potential to impact wastewater. 

Wastewater treatment technology: Many coal-fired plants use ash ponds, which are 

primarily designed for ash disposal, but which also provide some treatment. Some 

facilities use constructed, tank-based treatment for some or all wastewater streams. 

Water supply quality: A plant's source water can have a significant impact on some 

parameters, especially when considering the low levels present in ash pond discharges. 

• Cooling towers and condensers: The presence of cooling towers aids in mitigating 

thermal increases but may contribute trace metals from the cooling tower materials. The 

metallurgy of the condenser will also impact the trace metal contribution. 

• Boiler type: Within coal-fired power plants, the type of boiler will influence the 

wastewater characteristics in that different amounts of water will be needed to sluice 

bottom or fly ash. Pulverized coal plants generate a split of approximately 75% fly ash 

and 25% bottom ash, while cyclone boilers will generate a split of 25% fly ash and 75% 

bottom ash. In addition, pulverized coal and cyclone boilers will produce differing fly 

ash characteristics. Bottom ash also tends to be heavier and more chemically inert than 

fly ash. 

Our review of the available data and comparison with the overall industry identified the 

following gaps and analytical needs: 

Most of the PISCES field study sites were located in the southern US; however, other 

facilities are located in this as well as other regions of the country. The focus of the studies 

was with fly ash ponds, and thus sites that wet sluiced fly ash. Only one site employed dry 

ash handling. Power plants burning western, sub-bituminous, and lignite coals are not 

represented in this study. 

The PISCES field studies were conducted in the late 1990s, and at that time, few power 

plants employed SCR/SNCRs and only a fraction employed wet FGDs. With the CAIR and 

CAMR air regulations, many power plants are now installing SCRs as well as new "state-ofthe-art" FGDs. New FGDs, and specifically FGDs which employ limestone as the reagent 

and use forced oxidation to produce a gypsum product are not represented in the PISCES 

studies. 

Sites using fuels other than coal were not included. There are several thousand steam 

electric utility sites firing other fuels such as oil, natural gas, or refuse-derived fuel, as well 

as nuclear generating units. 

The PISCES studies were conducted approximately 10 years ago, employing the "state-ofthe-art'' sampling and analytical methods -at that time. Analytical methods have evolved; 

particularly for Se and As speciation. There is a better understanding of the complexities of 

sampling and analysis for Se and As speciation. For Se there is a trend toward using 

hyphenated methods (IC-ICP /MS) and away from hydride generation (EPA 1632). These 

6 3/9/2007 
analytical methods require further evaluation and the appropriate method(s) should then be 

applied to obtain a consistent, high-quality database. 

Sampling and Analytical Methods: Lessons Learned 

The 7 PISCES field studies provide many useful insights in conducting future sampling and 

analytical studies. Detail guidance is being provided to EPA in a separate report "Sampling 

and Analytical Plan Guidance for Water Characterization of Coal-Fired Steam Electric 

Utility Facilities". This section provides a brief summary of some of the key issues: 

• Analytical procedures including arsenic and selenium speciation methods 

• Clean versus conventional sampling methods 

• Solids digestion 

• Laboratory contamination from glassware (boron contamination) 

Analytical Procedures including Arsenic and Selenium Speciation 

The methods utilized during the PISCES program in the 1990s included some of the newest 

"cutting edge" methods under development by the EPA and specifically selected analytical 

laboratories. These were the "1600 series" methods which complemented traditional 

methods of analyses from EPA SW-846, such as method 6010 (Inductively Coupled Plasma 

Emission Spectroscopy - ICPES), and the 7000-series methods for Graphite Furnace Atomic 

Absorption Spectroscopy (GF AAS). 

Sample preparation for the ICPES and GFAAS (SW846, 6010B and 7000 series) methods 

were taken from the SW-846 3000-series methods (digestion techniques) which were 

determined based on the matrix. These digestion methods and the analytical method have 

not changed significantly since the 1990s. 

Each of the 1600-series methods includes self-contained preparation techniques within the 

procedures section. From the 1990s to present, these. methods have not changed 

significantly; many of the methods were then, and are currently, appended by the letter "M" 

to suggest aslight intralaboratory (which was also often interlaboratory) slight modification 

to the DRAFT 1600 series methods. All of these methods were "performance-based". The 

methods used during the PISCES study include: 

• EPA 1631(M)- Mercury (and Methyl-Mercury) by Cold Vapor Atomic Fluorescence 

Spectroscopy 

• EPA Method 1632(M) - Determination of Arsenic and Selenium Speciation by 

Hydride Generation 

• EPA Method 1638(M) - Determination of Elements by Inductively Coupled Plasma 

Mass Spectrometry 

These 1600-series methods are still utilized by laboratories and many are still appended by 

the "M", as modified. All analytical methods are influenced by the matrix which is prepared 

and analyzed. 

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The arsenic and selenium speciation method used in the PISCES studies (EPA 1632(M) ), is 

an operationally-defined method that is still used for arsenic and selenium speciation. The 

method has not been modified since the late 1990s when the PISCES data were collected. 

Potential matrix interferences may bias a measurement high or low depending on the type 

of matrix interference. Certain water streams such as those with high suspended solids may 

cause such matrix interferences. 

Recently, laboratories that specialize in metal speciation analysis have adopted analytical 

techniques (not limited to metals) which place different instrumental techniques in series to 

obtain better specificity for metal species and to reduce interferences and/ or enhance 

detection limits. The combination of ion exchange chromatography or high pressure liquid 

chromatography with inductively coupled plasma mass spectrometry (IC-ICP-MS or HPLCICP-MS) allows the analyst to quantify complex arsenic and selenium species that may have 

an impact on arsenic and selenium fate in power plant treatment systems. Some of the 

selenium forms identified in utility wastewaters using these methods include selenocyanate, 

methylseleninic acid, and various unidentified selenium compounds. 

Clean versus Conventional Sampling and Analytical Methods 

Two distinct sampling and analytical methods were used for sampling in the PISCES study: 

clean and conventional. Clean sampling and analytical methods for metals were used, and 

are recommended, at locations where concentrations of metals were expected to be near or 

below detection limits of conventional methods. Conventional methods were used for 

streams with higher levels of metals. Clean methodologies refer only to trace metals 

sampling and analysis. 

Clean methods consisted of the EPA Method 1669 "clean" sampling protocols and 1600-

series low-level analytical techniques. Locations using clean methods included the plant 

intake, cooling water, source water, and ash pond water. 

The conventional analytical methods (due to their lack of sensitivity at low levels) were 

found to more frequently have results considered potentially false positives (Type I, alpha 

errors) because they were measured at or near the method detection limit. For example, ash 

pond water collected using clean methods reported 0.07 J.Lg/L of cadmium (reporting limit 

of 0.011 J.lg/L), while using the conventional method in a side-by-side collection reported 0.5 

J.lg/L with a reporting limit of 0.18 J.lg/L. It is suspected that the clean result is more 

accurate because the conventional result is near its detection limit. The conventional 

method also had more contamination of samples for more commonly seen metals such as 

copper and zinc. 

Analysis of data collected in the PISCES studies, in which state of the art "clean" sampling 

and analytical techniques were used, indicated that historical data for ash pond mercury, 

copper, and zinc were likely biased high as is shown in Figure 1. This bias was probably 

due to contamination or method inaccuracy. Table 2 includes a summary of reporting 

limits for trace metals based on both the clean and conventional methods. The reporting 

limits for clean methods are generally much lower than that of conventional analytical 

methods, so data can be obtained at lower levels. 

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Hg (ng/L) r-

~ - Historical literature data 

~-- ----

Cu (ug/L) : ~·--·~a····~ D -PISCES Field Studies, conventional 

0 -PISCES Field Studies, clean 

+-

Zn (ug/L) 1 

_L_J_!__i-'-lJ+--- _ -· Li__Ll_C __ __J__J_ ~ _ "------L_L _ ~'"-'---

1'0 100 1 ,000 10,000 

5th to 95th Percentile Range of Effluent Concentrations 

Figure 1 

Difference Between Historic Literature and PISCES Field Studies Data 

Solids Digestion 

The analytical and preparation method in early rounds of the PISCES program (SW-846 

digestion method 3050A) used during ash analysis resulted in incomplete digestion of ash, 

which provided low-biased results for several parameters. A modified method for ash 

digestion was subsequently performed (ASTM D 3682) and is recommended for future ash 

analyses. 

9 31912007 
Table 2. Reporting Limit Ranges for Clean and Conventional Methods for Trace Metal 

Analyses in Ash Pond Effluent 

Parameter Conventional Method Clean Method 

Range of Re~orting Limits Range of Re~orting Limits 

{gg[!J L!!91Y 

Antimony 1.0-21 0.001-0.03 

Arsenic 0.88-125 0.018-2.0 

Beryllium 0.088-1.0 0.002-0.149 

Cadmium 0.1-2.8 0.002-0.08 

Chromium 0.45-8.4 0.0102-0.54 

Copper 0.84-10.0 0.005-0.16 

Lead 1-43.6 0.0073-0.69 

Mercury 0.082-0.2 0.000024-0.2 

Molybdenum 10-20 0.002-0.0449 

Nickel 1.0-6.4 0.0044-0.055 

Selenium 1.0-650 0.0059-1.8 

Silver 0.31-10 0.002-0.063 

Thallium 0.002-19 0.00075-0.01 

Vanadium 0.39-10 0.015-0.33 

Zinc 0.62-10 0.0054-1.02 

Laboratory Contamination from Glassware (Boron Contamination) 

Questions were raised after the PISCES program about whether boron leaching from 

laboratory glassware (borosilicate) may have biased the wastewater characterization high. 

Blanks were found to contain up to 294 r.tg/L of boron. Approximately 25% of the blanks 

collected actually resulted in boron detections. In evaluating PISCES data, results less than 

five times the maximum blank contamination are considered questionable due to possible 

blank contamination. The median ash pond effluent data was below five times the 

maximum blank detection, which may indicate some blank contamination. Ash pond 

effluent water had levels of boron with a median of roughly twice the maximum blank 

contamination. Therefore, the ash pond samples may be biased high. Fly ash sluice water 

and FGD wastewater typically had boron concentrations well above that found in blanks, 

but may also be somewhat affected by the potential for boron contamination. 

Based on the re-analyses of the PISCES data, future work should instruct the laboratory to 

avoid the use of borosilicate glassware during analyses of water samples for low levels of 

boron. 

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